The overall objective of this project is to understand how spatial patterns of differentiation are controlled during the normal development of animals and after injury--the processes of pattern formation and pattern regulation. The systems under study are the embryo and imaginal discs of Drosophila and the regenerating appendages of amphibians. In these systems pattern formation and regulation are associated with cell proliferation, and part of our objective is to understand how this growth is controlled. We propose an analysis of the genetic and epigenetic mechanisms which cause embryonic cells to embark on developmental pathways leading to imaginal disc formation; a study of the relationship between wound healing, growth, and pattern regulation in imaginal discs; and an analysis of the relationship between pattern formation and regeneration in amphibian limbs. We use Drosophila in our investigations because of our conviction that the resolution of these problems will require the use of genetic mutations and genetic techniques which are available only in this organism. We are using amphibians because their limbs regenerate well, even though they are homologous to mammalian limbs.